The prion diseases are a group of neurodegenerative disorders of animals and humans which may be both transmissible and inherited. They are associated with an abnormal form, designated PrPsc (scrapie form of the prion protein), of a normal cellular protein designated PrPc. Prions are unique in that, as an infectious pathogen, PrPcs is a protein devoid of nucleic acid. The nature of the structural difference between PrPc and PrPsc is clearly fundamental to understanding the modus operandi of the prion. One approach to elucidating this difference involves raising antibodies that are capable of distinguishing the isoforms. The aim of this project is to exploit combinatorial antibody library technology to generate monoclonal Fab fragments against scrapie, cellular and mutant forms of prion proteins. The advantages of this new technology over conventional hybridoma technology are that many more antibodies can be examined, that one is not restricted to immunizing rodents, that strategies can be designed to select antibodies of narrowly designed specificity and that antibody specificity can be readily manipulated genetically. The antibodies generated will be used to study the conformational changes associated with conversion of the cellular to the infective scrapie form of the prion protein, to compare mutant and native prion proteins and as immunohistochemical probes for prion proteins. Combinatorial libraries will be generated from mice and rabbits immunized with selected prion antigens including Syrian hamster, mouse and human PrPsc and PrPc. Semi-synthetic libraries will also be used. The libraries will be panned against diverse prion antigens including peptides and cryostat sections of scrapie brain. Judicious combination of immunogen and panning agent should allow selection of antibodies with the desired properties e.g. the ability to distinguish scrapie and cellular or mutant and wild type forms of PrP.